1. Field of the Invention
This invention generally relates to a data communication apparatus using a telephone network as a transmission line, and, more in particular, to a data communication apparatus having a dual function as a telephone unit and a facsimile unit.
2. Description of the Prior Art
In a small-scale office or at home, it is often the case to use a single telephone line not only for audio communications, but also for data communications for use in personal computers and facsimile machines. In such a case, it is conceivable to provide a structure in which a telephone line normally connected to a telephone unit is switched to a personal computer or a facsimile machine only when data communication is to be carried out. However, in such a structure, when a call is received, it is necessary for the operator to pick up the telephone receiver and ask the caller the object of placing a call. And, if the caller wishes to send information in a data communication mode, the operator has to manually operate a switch to connect the telephone line to a personal computer or facsimile machine. This is cumbersome because it involves a manual operation and the operator has to answer the telephone call every time when a call has been received.
Alternatively, it is also conceivable to connect the telephone line normally to a facsimile machine having an automatic receiving function. In such a case, when the caller wishes to send information in a facsimile transmission mode, desired information may be received by the facsimile machine automatically, so that this is advantageous because the operator at the receiver side is not required to answer a call. In this case, however, a problem arises when the caller wishes to carry out a verbal communication. That is, in such a facsimile machine having an automatic receiving function, when it receives a call in an automatic mode, the facsimile machine repetitively carries out transmission of a predetermined communication procedure signal to the calling station and reception of a response signal from the calling station responsive to that procedural signal. In the present case, however, since such a response signal is not transmitted, the above-mentioned sequential steps of transmission of a transmission procedural signal and establishment of reception of a response signal are repetitively carried out for a predetermined time period, e.g., 30 seconds, and, thereafter, a buzzer for indicating an operator call is activated. Then, at the called station, the operator will recognize that the calling station is requesting a verbal communication by this activation of a buzzer, so that the operator picks up the telephone receiver and then depresses a stop button of the facsimile machine. As a result, the telephone line is switched to the telephone unit, so that a verbal communication can be carried out.
As described above, the caller must wait for a relatively long period of time, e.g., 30 seconds in the above-described example, after having established a connection with the called station so as to establish a verbal communication mode, which is disadvantageous. Accordingly, in the prior art data communication apparatus having a dual function of verbal and data communications, there were various disadvantages, such as requiring to carry out a manual switching operation or a relatively long wait time period.